Major Winter Storm to Slam Mid-Atlantic and Northeast Midweek

(The Washington Post) -
The Old County Road in Greenwood, Maine is covered in snow Sunday, Dec. 6, 2020, after the first major winter storm of the season brought heavy, wet snow and high winds to the region. (Andree Kehn/Sun Journal via AP)

A major winter storm is set to wallop the Mid-Atlantic and the Northeast on Wednesday and Thursday, with many areas from western Virginia to southern New England expected to see heavy snowfall. But for the immediate Washington, D.C., area, a messy mix of precipitation is more likely than a major snowstorm.

The storm will take the form of a classic nor’easter, forming near the coast of the Carolinas and crawling up the Mid-Atlantic coast. An area of high pressure over eastern Canada will feed cold air into the storm, and many models show the potential for at least six to 12 inches of snow from west-central Virginia through eastern Pennsylvania into New York City and perhaps into southern New England, including Boston.

But just to the east of this zone, which includes Washington, Baltimore and the eastern suburbs of Philadelphia, enough mild air from the ocean may get drawn inland for snow to flip to ice and rain, limiting accumulations. That said, as the storm pulls away Wednesday night into early Thursday, these areas could see rain and mixed precipitation change back to snow before ending.

The exact position of the rain-snow line is still coming into focus, and there is some chance that it holds just to the east of Washington and Baltimore, which would allow for more significant snowfall in these cities and their close-in suburbs.

It is fairly likely that precipitation begins as snow between sunrise and noon Wednesday in the Washington region, except for cold rain in Southern Maryland. During the afternoon, the rain-snow line is likely to push northwest. The question is how far. The range of possibilities spans from Interstate 95 to Interstate 81.

If the rain-snow line doesn’t make much westward progress, this could become a significant snow event for most of Washington’s western suburbs and even in the city. Precipitation is likely to be heavy Wednesday afternoon and evening. But if the rain-snow line scoots toward the mountains, snow amounts will be limited and cold rain will prevail from I-95 eastward with a messy mix in between.

Even if a lot of snow doesn’t materialize west of Washington, low-level cold air may prove difficult to dislodge, creating the possibility of significant sleet or freezing rain. Toward Interstate 81, where mostly snow is likely, at least six to 12 inches is a good bet.

Where precipitation changes to rain and mixed precipitation in the Washington region, it could transition back to snow as the storm pulls away, with accumulation possible overnight Wednesday.

While the storm looks like a complicated forecast in D.C. itself, the big cities to the north and east that are closer to the cold air source and will be further north and west of the low-pressure area are under a greater threat for heavy snow.

In Philadelphia, there is the potential for six to 10 inches of snow, depending on the storm’s exact track and intensity, though the National Weather Service notes that mixing with sleet and rain could hold amounts down, especially in parts of New Jersey. Philadelphia’s northwestern suburbs could see a foot or more of snow.

New York may be in one of the storm’s sweet spots, with heavy snow, little mixing with sleet or rain, and strong winds. The Weather Service is not yet predicting specific snowfall amounts for the Wednesday storm, but multiple computer models support totals up to or even exceeding a foot, especially from the city on to points north and west.

In Boston, a cold, fluffy snow is likely, but there are questions about whether the heaviest snow bands will make it far enough north to affect the Boston metro or be confined further south.

“This is not a lock,” the Weather Service forecast office in Boston stated in a forecast discussion Sunday morning. At the same time, forecasters stated that the odds of accumulating, potentially heavy snow are increasing there. Six inches or more of snow is likely for much of southern New England, particularly in eastern Massachusetts, as well as much of Connecticut and Rhode Island.

Coastal flooding may also be a concern along the New Jersey shoreline and in southern New England as winds pick due to the air-pressure gradient between the high-pressure area to the north and the coastal low to the south.